Axon degeneration occurs after nervous system injury and during neurodegenerative diseases but very little is known about how injured or diseased axons destroy themselves. Recent work on the mouse Wallerian degeneration slow molecule (Wlds), which potently protects severed axons from degeneration, has revealed that axon degeneration is an active process of axon auto-destruction. Amazingly, Wlds can also suppress axon degeneration after chemical insult and delay disease onset in a number of mouse models of human neurodegenerative disease. Wlds is therefore a broadly neuroprotective molecule and understanding its molecular action is of paramount importance. We have developed the first Drosophila model to study injury-induced axon degeneration and shown that mouse Wlds can also potently suppress axon degeneration in severed Drosophila axons. These data indicate that the molecular mechanism that drive axon auto-destruction after injury are well-conserved in Drosophila and mammals, and open the door to powerful molecular-genetic approaches only available in Drosophila to study axon auto-destruction. In this proposal we will: (1) define the domains of the Wlds protein essential for it to protect axons;(2) determine whether Wlds interacts with the ubiquitin proteasome, NAD biosynthetic, or apoptotic machinery to block axon auto-destruction;and (3) perform the first ever forward genetic screens for mutation that block axon degeneration after injury or Wlds neuroprotective function. These studies represent the beginning of a long-term comprehensive effort to understand how axons destroy themselves after injury, and how Wlds impinges upon these pathways. We expect our findings to have a major impact on our understanding of axon degeneration after injury or during disease in humans, and the novel molecules we identify will be excellent candidates for therapeutic intervention in human axonopathies. PUBLIC HEALTH RELEVANCE: After brain injury or during neurological disease neuronal fibers degenerate, connections in the brain are lost, and neural function is irreversibly compromised. We are studying the cellular action of an extraordinary molecule, WldS, which suppresses this loss of neuronal fibers. Our work will identify many new molecules that will be targets for treatment of patients after brain injury or during neurological disease.